Answer: I can't answer this
Step-by-step explanation:
Use the internet it helps a lot
It sounds like initially we have a total of 18*5 = 90. Then we are adding 5 + 4 +3 +2 +1 to this.
so that gives us 105.
105/5 = 21
Answer: 
Step-by-step explanation:
We know that the general form of the exponential decay formula is
, where y is final amount remaining after t time, A is the original amount and r is the rate of decay
Now, the ratio of strontium-90 remaining, p , as a function of years, t , since the nuclear accident. 
Hence, the ratio of remaining since the nuclear accident is 